1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, and more particularly, to a method of manufacturing a semiconductor device having a buffer coating film and a passivation film serving as a surface protective film.
2. Description of the Background Art
FIGS. 3A to 3F are views for describing a conventional method for manufacturing a semiconductor device having a passivation film and a buffer coating film.
A conventional method for manufacturing a semiconductor device will now be described.
First, as shown in FIG. 3A, an aluminum interconnection 2 is formed on a semiconductor substrate 1. Here, although not shown, semiconductor elements are formed on the semiconductor substrate 1.
Next, as shown in FIG. 3B, a passivation film 3 formed from SiO2 or Si3N4 is formed on the entire surface of the semiconductor substrate 1 containing the aluminum interconnection 2.
Next, as shown in FIG. 3C, a buffer coating film 4 is formed on the passivation film 3. Here, polyimide having superior moisture resistance and chemical resistance is used for the buffer coating film 4. Varnish formed by dissolving polyamic acid, which is a precursor of polyimide, with an organic solvent is applied on the passivation film 3 by means of spin coating.
Next, as shown in FIG. 3D, the polyimide film 4 is patterned by means of a known photolithography technique.
Here, if employed polyimide is non-photosensitive, photoresist is formed on the polyimide film 4. Then, the photoresist is subjected to exposure and development, thereby forming a desired photoresist pattern. Subsequently, the polyimide is subjected to etching with the photoresist pattern as a mask, thereby forming a desired pattern.
In contrast, if employed polyimide is photosensitive, the photoresist is unnecessary. Namely, after formation of the polyimide film 4 on the passivation film 3, the polyimide film 4 is subjected to exposure and development. Thereby, a desired pattern is formed.
Next, after patterning of the polyimide film 4, the polyimide film 4 is cured at 300xc2x0 C. through 450xc2x0 C. for the purpose of transforming polyimide into imide and vaporizing a solvent. Further, in the case of photosensitive polyimide, the polyimide film 4 is cured for the purpose of vaporizing a photosensitive group in addition to the above-described purposes. As a result, as shown in FIG. 3E, there is formed a polyimide film 4A.
Finally, as shown in FIG. 3F, the passivation film 3 is etched while the cured polyimide film 4A is taken as a mask, thus exposing the aluminum interconnection 2.
As mentioned above, the conventional method of manufacturing a semiconductor device comprises the foregoing steps. The passivation film 3 is etched while the cured polyimide film 4A is taken as a mask. Polyimide undergoes a volumetric shrinkage of about 50% when being cured. Before being cured,the sidewall of the polyimide pattern is substantially vertical, as shown in FIG. 3D. In contrast, after having been cured, the sidewall becomes tapered; for example, as shown in FIG. 3E.
When the passivation film 3 is etched while the cured polyimide film 4A is used as a mask, the polyimide film 4Axe2x80x94which is located in the vicinity of the passivation film 3 and has a small thicknessxe2x80x94is also etched away along with the passivation film 3. As a result, the finished dimension of a portion 3A of the passivation film 3 to be etched becomes difficult, thus resulting in variations in the finished dimension.
The present invention has been conceived to solve the previously-mentioned problems and a general object of the present invention is to provide a novel and useful method of manufacturing a semiconductor device.
A more specific object of the present invention is to provide a method of manufacturing a semiconductor device which enables an improvement in the dimension control of a portion of a passivation film to be etched.
The above object of the present invention is attained by a following method of manufacturing a semiconductor device.
According to one aspect of the present invention, in a method of manufacturing a semiconductor device, an interconnection is formed on a semiconductor substrate having a semiconductor element formed thereon. Next, a passivation film is formed on the semiconductor substrate including the interconnection. Further, a polyimide film, which is served as a buffer coating film, is formed on the passivation film. Further, the polyimide film is patterned. Next, the passivation film is subject to etching while the patterned polyimide film is taken as a mask. Next, a hardened layer, which is formed on the surface of the polyimide film as a result of etching, is removed through ashing. Next, the semiconductor substrate is cured after ashing so as to transform the polyimide film into imide.
Accordingly, since the semiconductor substrate is cured after etching, the dimensional accuracy of processing of a passivation film can be improved.
Further, since the semiconductor substrate is cured after ashing, quality of the polyimide film can be improved.